Frequency sorter, and frequency locker for monitoring frequency shift of radiation source

An apparatus for locking the frequencies of a plurality of radiation sources substantially to predetermined equally spaced frequencies spaced apart by a predetermined frequency spacing, comprising:

• one or more frequency lockers, the locker or each of the lockers having equally spaced periodic frequencies with a free spectral range (FSR) substantially equal to the predetermined frequency spacing,
• means for passing radiation from each of the sources through the locker or one of the lockers;
• one or more first detectors detecting radiation passed by the locker or one of the lockers to provide first outputs;
• and
• means for adjusting the frequency of each of the sources in response to said first outputs.

A frequency sorting device, comprising:

• an etalon having an optical path length that is accurate to about 0.5 microns or better;
• an input optical fiber supplying radiation to the etalon;
• and
• an output optical fiber delivering radiation from the etalon.

A frequency sorting method, comprising:

• providing an etalon having an optical path length that is accurate to about 0.5 microns or better;
• supplying broad band radiation to the etalon;
• and
• delivering from the etalon radiation having periodic peak frequencies with a frequency spacing.

A frequency sorting method, comprising:

• providing an etalon having an optical path length that is accurate to about 0.5 microns or better;
• supplying radiation within a pass band to the etalon;
• and
• delivering radiation having a narrower band width than the pass band from the etalon.

A method for making an etalon, comprising:

• determining a desired optical path length for the etalon;
• providing two reflective surfaces;
• and
• adjusting the optical path length of the etalon, said adjusting including changing a distance between the surfaces or altering an angle of incidence of a beam of radiation on said surfaces so that an optical distance through an optical medium between the surfaces is substantially equal to the desired optical path length, said changing including thin film deposition or etching.

A multiplexer system comprising:

• a plurality of radiation sources providing radiation at predetermined equally spaced frequencies spaced apart by a predetermined frequency spacing;
• a plurality of optical channels, each channel conveying radiation from a corresponding source to a wavelength division multiplexer or from a wavelength division demultiplexer;
• a frequency locker having equally spaced periodic frequencies with a free spectral range (FSR) substantially equal to the predetermined frequency spacing for detecting a frequency shift of radiation from each of the sources and to provide an output;
• splitters, each splitter diverting a percentage of radiation from a corresponding optical channel;
• a multi-channel switch sequentially providing radiation diverted by one of the splitters to the frequency locker to sequentially detect a frequency shift in the plurality of sources;
• and
• means for adjusting frequencies of the plurality of sources in response to the output.